1. Field of the Invention
This invention relates broadly to analytical instruments. More particularly, this invention relates to an analyzer apparatus for determining when a photometric change occurs in a sample, and relating the change to a condition of the sample at a previous time.
2. State of the Art
Water quality, and particularly bacterial content in water is of great concern. Municipalities perform periodic checks of water quality to ensure that water reserves are safe. Recently, home monitoring of water quality has become popular.
A number of products are available for testing water quality. One variety of product is an ampoule which is a sealed evacuated vial containing a powdered nutrient for microbes and an indicator which changes color when the concentration of microbes reaches a specific high level. One such ampoule is shown in U.S. Pat. No. 5,935,799 to Isbister. In use, a user inverts the ampoule in a cup of sample water and breaks off a scored tip of the ampoule. The vacuum in the ampoule causes the ampoule to fill with sample water. The ampoule is then shaken to mix the powdered nutrient and indicator with the water. Finally, the ampoule must be maintained at a constant temperature, e.g., 34xc2x0 C., for a relatively long period of time, e.g., up to 12 hours. One manner often suggested by manufacturers of the ampoules for maintaining proper temperature is for the user to place the ampoule in a shirt pocket of the user, since the shirt pocket is approximately at the desired temperature. Periodically, e.g., every thirty minutes, the user must look for the indicator to change color by holding the ampoule up the light and comparing the observed color against a printed chart. When the color change is observed, the elapsed time is recorded and a second chart is used to look up the number of microbes that were in the original sample water based upon the recorded time.
The determination of the number of microbes is based on the fact that microbes multiply by binary fission. The number of microbes in the original sample may therefore be determined by reference to an exponential chart and the recorded time.
While this type of analytical product is useful, it has several drawbacks. One problem is the requirement to hold the ampoule in a shirt pocket for incubation. Another problem is that the accuracy is questionable, as human judgment is required to read the color at the end point.
Several apparatus have been disclosed to test samples, but they do not address the testing requirements for the above described ampoules. For example, U.S. Pat. No. 5,013,155 to Rybak discloses an apparatus which determines a specific color of a sample in a vial received in a receptacle in the apparatus. The device uses two light sources, each of a different color, which are alternatingly pulsed, and respective photodetectors. The results are interpolated along with signals present when no light is emitted, to identify the specific color of the test sample. The Rybak apparatus requires a vial of clear distilled water to calibrate the instrument. In addition, the device is not adapted for heating test vials at a constant temperature.
U.S. Pat. No. 5,959,738 to Hafeman et al. uses either a single light source capable of operating at multiple wavelengths, or multiple and different wavelength light sources. A relationship is determined between the light absorption properties of a liquid sample (solvent and analyte) and the optical pathlength of the liquid sample to calculate a concentration of an analyte in a solvent of the sample. The device is not capable of determining when a change occurs in the contents of an ampoule when the contents of an ampoule are already known.
Therefore, what is required is a device adapted to determine biological activity as a result of a decrease in light passage through a sample over time.
It is therefore an object of the invention to provide a apparatus for determining when a particular change in the contents of an ampoule occurs via photometric measurements.
It is another object of the invention to use a single wavelength light source which functions as both a reference beam and a measuring beam.
It is a further object of the invention to provide an apparatus which centralizes all componentry of the light emission and detection system.
It is an additional object of the invention to provide an apparatus which is substantially free from error due to ambient light.
It is a also an object of the invention to provide an apparatus which determines at time at which a targeted photometric change occurs in an sample, and relating the targeted change to a condition of the sample at a previous time.
It is yet another object of the invention to provide an apparatus which maintains ampoules at a desired temperature.
It is yet a further object of the invention to provide a portable and relatively low cost apparatus for heating and analyzing changes in the contents of an ampoule.
In accord with these objects, which will be discussed in detail below, an ampoule analyzer apparatus is provided which includes a housing having at least one receptacle (or nest) for an ampoule, a cover for substantially preventing ambient temperature and light from affecting each receptacle, a light analysis system, an incubation system, and a master control system.
The light analysis system includes, for each receptacle, at least one light source and a photodetector positioned such that the light from the light source passes through the receptacle (and thereby the ampoule and its contents) prior to entering the photodetector. The light source is chosen to deliver a predetermined wavelength of light such that the color change of the contents of the ampoule causes reduction in the intensity of the light transmitted through the contents of the ampoule.
The incubation system includes, for each receptacle, a heating element which rapidly heats the receptacle to a desired temperature and a temperature sensor which senses the temperature of the receptacle. Each receptacle is preferably insulated to prevent unintended heating of neighboring receptacles of the apparatus.
The master control system permits user input, operates the light analysis system and the incubation system. In addition, the master control system includes a timer, and a memory provided with a look-up table relating the type of test, the time to test completion, and the associated bacterial count at the start of the test. A user-readable display for the output of the results, e.g., the bacterial count at time zero, is also provided.
During operation, an ampoule containing a water sample and a reagent which causes the sample to change color when a certain level of biological activity is present in the sample is placed within one of the receptacles. The light analysis system is operated to transmit light at the predetermined wavelength through the ampoule (either axially or transversely) to the detector, and a maximum amount (intensity) of light passing through the ampoule is determined. The incubation system is also operated to heat the receptacle and the ampoule therein to a desired test temperature and the timer is started. The light analysis system periodically transmits light through the ampoule. Increased biological activity in the sample causes a color change to the indicator which reduces light transmission through the ampoule. When the light detected at the detector is reduced relative to the light transmitted by a predetermined percentage of the maximum amount of light, the master control system signals that the test is complete. Based on the amount of time required for this to occur, the master control system determines from the look-up table the bacterial content in the sample at the beginning of the test and displays the results on the display.
The apparatus may include a large number of receptacles suitable for laboratory use or may include fewer or one receptacle suitable for home or portable use.
Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures.